The construction and operating conditions of a blast furnace are well known, but anyone uninformed can refer to Chapter 12 of The Making, Shaping and Treating of Steel, Seventh Edition, copyright 1957 by the United States Steel Corporation, which is hereby incorporated by reference in the following.
Usually a blast furnace is lined with fired bricks throughout its area receiving abuse from heat and abrasion, but when repairs are required, a refractory concrete, while moist and plastic, can be injected into the areas requiring repair, followed by drying and annealing of the concrete. The chemical compositions of two known concretes are as follows:
Mass A: SiO.sub.2 36.3%, Al.sub.2 O.sub.3 54.2%, TiO.sub.2 2.1%, Fe.sub.2 O.sub.3 1.3%, CaO 5.1%, Na.sub.2 O 0.12%, K.sub.2 O 0.27%, P.sub.2 O.sub.5 0.06%, annealing loss 0.43%. PA0 Mass B: SiO.sub.2 6.1%, Al.sub.2 O.sub.3 81.5%, TiO.sub.2 2.2% Fe.sub.2 O.sub.3 1.8%, CaO 7.2%, Na.sub.2 O 0.10%, K.sub.2 O 0.04%, P.sub.2 O.sub.5 0.04%, annealing loss 0.67%. PA0 A. 10 to 30% by weight of a mineral alkaline earth compound selected from the class consisting of metallurgical slags containing calcium-mono-aluminate, calcium-di-aluminate and calcium-silico-aluminate, alumina-containing cements of the type calcium mono-aluminate and calcium di-aluminate, alumina-containing silicate cements, silicates of calcium or barium, and alkaline earth oxides selected from the class consisting of magnesium oxide, dolomite, calcium oxide and barium oxide; PA0 B. 14 to 54% by weight of a compound selected from the class consisting of silicon oxide, chromium oxide, titanium dioxide, zirconium oxide and aluminum oxide having a particle size of from 100 A to 0.1 .mu.m; PA0 C. 14 to 54% by weight of an inert filler material with a particle size of from 1 to 100 .mu.m; PA0 A. 10 to 30% by weight alumina-containing cement or alumina-containing slag, PA0 B. 14 to 54% by weight chromium oxide with a particle size of between 100 A and 0.1 .mu.m, PA0 C. 14 to 54% by weight fired aluminum oxide with a particle size of between 1 and 100 .mu.m;
The durability of such injected concrete lining masses is substantially less than that of the fired bricks, but concrete can be used for repairs. Refractory concrete can also be used as small volume masses in blast furnaces at the downcomer connections with the furnace's gas hood, for the installation of the bosh cooling plates, at the iron and cinder notches and at other locations.
However, although known refractory concretes have a high strength at room temperatures, during heating between 700.degree. and 1100.degree. C., depending on the type of cement, a zone of relatively low strength is formed which only achieves a high final strength when ceramic fusion of the concrete is attained. Because of this zone blast furnace lining concrete parts have been subject to a high degree of abrasion from the descending solids in the furnace whenever this zone of lower strength occurs.
For example, when the concrete parts have a volume of more than 0.2 m.sup.3, the inside towards the furnace heat is fused to a ceramic of high strength, whereas on the outside of the concrete parts somewhat away from the heating, a strength approaching the room temperature strength of the concrete prevails. That is to say, the concrete part is of high strength as to its inner and outer side portions but has the low strength zone between these high strength areas. The result is that under the furnace's operating conditions the concrete parts can tear apart under abrasion or impact.
Even during the drying of concrete parts when of relatively large volume have been known to become cracked or to disintegrate due to inner thermal stresses resulting from the drying heat.
Because of the foregoing knowledge of the disadvantages of refractory concrete when used as blast furnace lining parts of large volume, such as a volume greater than 0.2 m.sup.3, experienced blast furnace designers have considered refractory concrete to be unacceptable for such parts regardless of the possible advantage that it can be formed into finished parts prior to installation of the parts in the furnace lining construction. Concrete also has the advantage that it can be injected for the repair of the furnace lining brickwork, but only to provide masses of small volume as indicated.
Concretes using cement and aggregates of many compositions are known. All are resistant to heat and abrasion to some degree under some conditions, but in view of the long history of blast furnace lining technology, it would be surprising to find that any general purpose concrete could advantageously be used as replacement.
In the present instance, the object has been to provide a blast furnace having a refractory lining of concrete components each having a volume of at least 0.2 m.sup.3 and which is adequately resistant to the conditions existing inside of a blast furnace to permit its incorporation as a lining component for a furnace manufacturing pig iron, the concrete components being preformed prior to furnace lining installation, with a fixed shape and dimensions and which are in a condition for installation and satisfactory use as a part of the furnace lining.